Apparatus for mixing material

ABSTRACT

The invention relates to mixing apparatus in which the drive motor and the stirrers are each coupled to the three revolving elements of a planetary gear. In such apparatus the speed of the two stirrers is automatically adapted to the prevailing counter-moment.

The invention relates to mixing apparatus of the kind having two coaxialstirrers and a common motor for driving them.

Apparatus of the general class to which the invention relates is knownfor example from U.S. Pat. No. 2,209,287. In that apparatus, one stirreris coupled directly to the drive motor, whilst the other stirrer isdriven via the inner gear ring of a planetary gear in which the sunwheel is coupled to the drive shaft and the planet carrier is fixedstationary on the housing of the mixing apparatus. Consequently the twostirrers are driven at a fixed spaced and a constant speed ratio.

The disadvantage of such a construction is that when one stirrer has toovercome a particularly great moment of resistance, and in an extremecase comes to a standstill, the other stirrer is also incapable ofexerting a stirring effect.

The object of the invention, therefore, is to provide dual stirrermixing apparatus wherein the two stirrers operate in an optimum mannereven with differing and alternating moments of resistance.

In the mixing apparatus according to the invention the speeds of thestirrers are not fixed in advance but are automatically set as afunction of the counter-moment of the stirrers. If the counter-moments(i.e. the moments of resistance exerted on the stirrers by the materialto be mixed) alter, then the speeds of the stirrers are also altered sothat the stirrer encountering the least resistance rotates at anincreased speed that is higher than its initial speed. If in an extremecase one stirrer is brought to a standstill by an unusually great momentof resistance then the other stirrer goes at maximum speed.

If the external diameter and/or the tool cross-section of one stirrer ischosen so as to be greater than the external diameter and/or toolcross-section of the other stirrer, then basically the first stirrerruns more slowly than the second stirrer. Furthermore, the speed of eachof the two stirrers is adapted to the moment of resistance in each case.

The mixing tool according to the invention is also distinguished by anoptimum mixing effect even with material which is difficult to mix, andalso by low energy consumption and compact construction.

The invention is explained in greater detail below with the aid ofseveral embodiments which are illustrated in the drawings wherein;

FIG. 1 shows a partially cut-away overall view of the mixing apparatusaccording to the invention;

FIG. 2 shows an enlarged sectional view of a detail (corresponding tothe section II in FIG. 1) to explain a first embodiment;

FIG. 3 shows a sectional view of a detail similar to that of FIG. 2, butto explain a second embodiment;

FIG. 4 shows a variant (similar to FIG. 2) of a further embodiment;

FIG. 5 shows a partial representation of a further embodiment.

First of all the general construction of the mixing apparatus will bedescribed with the aid of FIG. 1. This mixinng apparatus is built on astand 1 on which is arranged a pillar or column 2 supporting a mixingvessel 3 which is constructed as a cylindrical vessel with a verticalaxis 3a. The base 4 and the peripheral wall 5 of this mixing vessel 3can be of double-walled construction and can have a heat exchange medium(e.g. cooling medium) flowing through them. A cover 6 closes off themixing vessel 3 towards the top, whilst a discharge pipe 7 or the likeserves for the discharge of the mixed material.

The drive shaft 9 of a planetary gear 10 which will be described ingreater detail below is supported and guided in at least one rollerbearing 8 inside the support 2. The planetary gear serves for the commonrotary drive of a lower stirrer 11 which is arranged near the baseinside the mixing vessel 3 and an upper stirrer 12 which is arrangedaxially spaced above the stirrer 11.

In this embodiment at least two blades 11a having the same cross-sectionand the same radial length are provided as stirrer tools for the lowerstirrer, and at least two blades 12a having the same length and the samecross-section are also provided as stirrer tools for the upper stirrer.

Whilst the upper end of the gear drive shaft 9 is coupled to theplanetary gear 10, the lower end of this drive shaft 9 is coupled via abelt drive 13 to a drive motor 14 which, depending upon the use forwhich the mixing apparatus is intended, can be a drive motor with aconstant speed or a drive motor with variable speed (e.g. a vario geardrive).

In this mixing apparatus the two stirrers 11 and 12 which are arrangedone above the other are intended to be driven by the planetary gear 10at selected different or relative speeds of rotation. For this purposeit is important first of all for the external diameter and/or the bladecross-section of the slower-running stirrer to be chosen so as to begreater than the external diameter and/or blade cross-section of thefaster-running stirrer.

In the embodiment illustrated in FIG. 1 it is assumed that the lowerstirrer 11 is the slow-running one and the upper stirrer 12 is thefast-running one. It can therefore be seen in the drawing that the lowerstirrer 11 has the greater external diameter, i.e. the radially outerends of the blades 11a extend to the immediate proximity of the innerface of the peripheral wall 5, whilst the external diameter of the upperstirrer 12 is kept substantially smaller than that of the lower stirrer11. In addition, the blades 12a of the upper stirrer 12 (as indicated onthe right-hand blades 12a in FIG. 1) have a smaller cross-section thanthe blades 11a of the lower stirrer 11; at least the blades 12a of thefaster-running stirrer 12 preferably have a fairly streamlinedcross-section.

In the embodiment described above of the two stirrers 11, 12 which lieone above the other, a greater counter-moment acts on the lower stirrer11 or the blades 11a thereof during the mixing operation than on theupper stirrer 12 or the blades 12a thereof.

A first embodiment of the planetary gear which drives the two stirrers11 and 12 will now be described with the aid of FIG. 2.

The planetary gear 10 contains a sun wheel 15 which is fixed (e.g.wedged) on the upper end 9a of the transmission shaft 9, an inner gearring 16 which is arranged coaxially therewith, at least two planetwheels 17 positioned in the annular space between the sun wheel 15 andthe inner gear ring 16 and in toothed engagement with both of thelatter, and a planet carrier 18 which retains these planet wheels 17 sothat they are freely rotatable.

In this embodiment the lower stirrer 11 has a lower hub 19 which is ofhollow construction and projects downwards with its lower end throughthe vessel base 4 and is mounted in this vessel base--suitablysealed--by means of roller bearings 20 so as to be freely rotatable. Thelower end section 19a of this lower hub 19 which projects out of thevessel base 4 is widened in the shape of a bell, and the inner gear ring16 of the planetary gear 10 is fixed in this lower end section 19a. Thusthe bell-mouthed lower end section 19a of the lower hub 19 surrounds thesun wheel 15, the planet wheels 17 and the planet carrier 18advantageously in the manner of a housing.

The planet carrier 18 which is for example of annular or circularconstruction and bears the planet wheels 17 so that they are freelyrotatable has a shaft 21 which is connected to it so as to be fixedagainst rotation and extends coaxially upwards through the hollow lowerhub 19, is supported and guided in this lower hub 19 by roller bearings22 so as to be freely rotatable and is connected with its upper end 21ato the upper hub 23 of the upper stirrer 12 so as to be fixed againstrotation (e.g. screwed or wedged on).

A second embodiment of the planetary gear 10' is illustrated in FIG. 3;for the sake of simplicity, in this second embodiment parts and elementswhich are of similar construction are designated by the same referencenumerals modified by prime, so detailed explanation thereof isunnecessary.

In this embodiment as shown in FIG. 3 the lower hub 24 of the lowerstirrer 11' is of hollow construction and is provided at one end, inthis case at its upper end 24a, with an inner gear ring 16' fixed in it,and in addition to this inner gear ring 16' the planetary gear 10'contains a sun wheel 15' which is fixed on the upper end 9'a of the geardrive shaft 9' (e.g. with the aid of an adjusting spring 25) and islocated coaxially inside the inner gear ring 16' and at the levelthereof, as well as at least two planet wheels 17' arranged in theannular space between the sun wheel and the inner gear ring and intoothed engagement with the latter two.

In this case the gear drive shaft 9' is mounted on the one hand insidethe lower hub 24 (below the sun wheel 15') by means of roller bearings26 and on the other hand at its upper end 9'a (above the sun wheel 15')in further roller bearings 27 centrally inside the upper hub 28 of theupper stirrer 12' so as to be freely rotatable in each case. This upperhub 28 is of cap-like construction and constitutes an upper, straight,approximately cylindrical extension of the lower hub 24, and isindependently rotatable with respect to the latter. This upper hub 28which is closed towards the top has an outer annular space in whichroller bearings 29 for freely rotatable mounting and support of theupwardly projecting axial extensions 17'a of the planet wheels 17' aremounted. In this way the cap-like upper hub 28 also forms the planetcarrier of this planetary gear 10'; in addition, the upper end 24a ofthe lower hub 24 and the upper hub 28 referred to above surround theessential gear parts of the planetary gear 10' like a housing.

As FIGS. 2 and 3 show, the common planetary gear 10 or 10' for the twostirrers is of extremely compact construction and relatively simpledesign. The planetary gear provides for automatic adaptation of thespeed of the two stirrers to the counter-moment occurring at the time.The two stirrers are driven in opposite directions.

If it is assumed, for example, that the planetary gear has atransmission ratio of 1:3 and the gear drive shaft rotates at a speed of1500 r.p.m., then the maximum speed difference between the two stirrersis 500 r.p.m.

If one assumes that the counter-moment acting on the blades of the lowerstirrer is infinitely great, so that the speed of this lower stirrer iszero, then in this case the upper stirrer rotates at a speed of 500r.p.m. in the same direction as the drive shaft.

In contrast to the embodiments described above, if required the lowerstirrer can be the faster-running one and the upper stirrer can be theslower-running one.

A particular advantage of the construction according to the inventionfrom the point of view of process engineering is that because of theautomatic adaptation of the speed of the two stirrers to thecounter-moment occurring at the time the energy to be used for themixing operation is introduced into the material to be mixedparticularly evenly and without localised overheating. On the otherhand, in known constructions the lower stirrers which are located nearthe base and constructed with a large stirrer cross-section frequentlyrun too fast in comparison with the upper stirrer.

If in the embodiments described above the drive shaft of the planetarygear is introduced into the mixing vessel through the base, it is ofcourse also possible within the scope of the invention to introduce thedrive shaft into the mixing vessel through the lid.

Whereas in the embodiments illustrated in FIGS. 1 to 3 the gear driveshaft 9 is coupled to the sun wheel 15 or 15' of the planetary gear,FIG. 4 shows a variant in which the gear drive shaft 9 is coupled to theplanet carrier 18 whilst the sun wheel 15 is connected to the upperstirrer 12 via the shaft 21 and the inner gear ring 16 is provided onthe hub 19 of the lower stirrer 11. In this embodiment the two stirrers11 and 12 are driven in the same direction. Here, too, there is anautomatic adaptation of the speed of the two stirrers to thecounter-moment acting on the stirrer in question.

Finally, FIG. 5 shows a variant in which the gear drive shaft 9 carriedthe inner gear ring 16 of the planetary gear, the sun wheel 15 of whichis connected via the shaft 21 to the upper stirrer 12 (not shown) andits planet carrier 18 is connected to the lower stirrer. In thisconstruction, too, the speeds of the mixing tools alter as a function ofthe prevailing counter-moments.

I claim:
 1. Mixing apparatus comprising a mixing vessel for containing aquantity to material to be mixed; at least two stirrers; means mountingsaid stirrers within said vessel for rotation about a common axis;common drive means for said stirrers; and drive transmission meanscoupling said drive means to said stirrers, said transmission meanscomprising planetary gear means having a rotary sun gear member, arotary ring gear member, and a rotary carrier member carrying rotaryplanet gears in mesh with the sun gear member and the ring gear member,means coupling said drive means to one of said members, means connectingone of said stirrers to another of said rotary members, and meansconnecting the other of said stirrers to the remaining one of saidmembers, said transmission means being responsive to the resistanceimposed by material in said vessel to the rotation of the respectivestirrers to adjust the speeds of rotation of said stirrers so that thestirrer encountering the least resistance rotates at the fastest speed.2. Apparatus according to claim 1 wherein said drive means is connectedto said sun gear member.
 3. Apparatus according to claim 1, wherein saiddrive means is connected to said planet gear carrier member. 4.Apparatus according to claim 1 wherein said drive means is connected tosaid ring gear member.
 5. Apparatus according to claim 1 wherein saidstirrers have different diameters, the diameter of one of said stirrersbeing greater than that of the other of said stirrers.
 6. Apparatusaccording to claim 1 wherein said stirrers have differentcross-sectional dimensions, the cross-sectional dimension of one of saidstirrers being greater than that of the other of said stirrers. 7.Apparatus according to claim 1 wherein one of said stirrers has a hollowhub at one end of which is fixed said ring gear member, and a shaftextending through said hub, said shaft being connected to said planetgear carrier member and to the other of said stirrers.
 8. Apparatusaccording to claim 7 wherein said hub acommodates therein at one endthereof said sun gear member, said planet gear, and said planet gearcarrier member.
 9. Apparatus according to claim 8 wherein said one endof said hub forms a bell-shaped housing.
 10. Apparatus according toclaim 1 wherein said coupling means comprises a drive shaft connected tosaid drive means, a first hub rotatably accommodating said drive shaft,a second hub extending in axial prolongation of said first hub, said sungear member being fixed to said drive shaft, said ring gear member beingfixed to said first hub, and said carrier member being rotatably mountedin said second hub.
 11. Apparatus according to claim 10 wherein one ofsaid stirrers is secured to said first hub and the other of saidstirrers is secured to said second hub.
 12. Apparatus according to claim1 wherein each of said stirrers comprises a plurality of blades, theblades of at least one of said stirrers having a streamlinedcross-section.
 13. Mixing apparatus comprising a vessel adapted tocontain a quantity of material to be mixed; at least two stirrers; meansmounting said stirrers in said vessel for rotation about a common axisand at a level to engage material therein; common rotary drive means forrotating said stirrers; and planetary gear transmission means couplingsaid drive means and said stirrers, said planetary gear transmissionmeans being responsive to the resistance imposed by material in saidvessel to the rotation of the respective stirrers to adjust the speedsof rotation of said stirrers so that the stirrer encountering the leastresistance rotates at the fastest speed.
 14. Apparatus according toclaim 13 wherein each of said stirrers has blades extending radiallyfrom said axis, the blades of one of said stirrers having a greaterradius than that of the blades of the other of said stirrers. 15.Apparatus according to claim 13 wherein said planetary gear transmissionmeans has a fixed drive transmission ratio greater than 1:1, therebyestablishing a maximum difference between the speeds of rotation of saidstirrers.
 16. Apparatus according to claim 15 wherein said ratio is 3:1.17. Apparatus according to claim 13 wherein said planetary geartransmission means comprises a rotary sun gear member, a rotary ringgear member, and a rotary carrier member carrying a plurality of rotaryplanetary gears in mesh with said sun gear member and said ring gearmember.
 18. Apparatus according to claim 17 wherein said drive means iscoupled to said sun gear member.
 19. Apparatus according to claim 17,wherein said drive means is coupled to said planet gear carrier member.20. Apparatus according to claim 17 wherein said drive means is coupledto said ring gear member.